The initiation of bone formation induced intrinsically by osteoinductive hydroxyapatities

Abstract:

The initiation of new bone formation within the porous spaces of
hydroxyapatite (HA) implants involves the expression of osteogenic
markers belonging to the TGF-β superfamily. To study the genetic
expression of these osteogenic markers in relation to the type of HA
implant used and implantation period, five different types of porous HA
biomaterials were implanted in the rectus abdominis muscles of adult
baboons Papio ursinus, and were harvested at two, three and 12 months.
The total RNA of all harvested samples was extracted and analysed using
the Northern blot technique. The results showed that Collagen type IV,
GDF-10 and BMP-7 were expressed at the early time points at relatively
high levels, and their expression levels were significantly reduced at 12
months. The expression of these makers was not affected by the type of
porous HA implant used. The histological sections of these specimens at
two and three months showed vascularised connective tissue within the
porous spaces of the implants with no bone formation. However, at 12
months there were substantial amounts of bone formed in all the studied
implants. The down-regulation of the expressed osteogenic markers at 12
months correlates to the amount of bone formed, suggesting some
negative feedback mechanism which may be acting via inhibitory Smads
proteins in relation to the amount of bone formed. Neither TGF-β1 nor
BMP-3 messages were detected in any of the studied samples, It is
possible that these bone markers are not expressed locally within the
vicinity of the porous HA implants but are adsorbed to the HA implants from
the circulatory system.

Description:

Faculty of Health Sciences,
Degree of Master of Science in Medicine.
9208366a